﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Text;

public partial class VerifyCode : System.Web.UI.Page
{
    static string[] FontItems = new string[] {   "Arial", 
                                                  "Helvetica", 
                                                  "Geneva", 
                                                  "sans-serif", 
                                                  "Verdana"
                                              };

    static Brush[] BrushItems = new Brush[] {     Brushes.OliveDrab,
                                                  Brushes.ForestGreen,
                                                  Brushes.DarkCyan,
                                                  Brushes.LightSlateGray,
                                                  Brushes.RoyalBlue,
                                                  Brushes.SlateBlue,
                                                  Brushes.DarkViolet,
                                                  Brushes.MediumVioletRed,
                                                  Brushes.IndianRed,
                                                  Brushes.Firebrick,
                                                  Brushes.Chocolate,
                                                  Brushes.Peru,
                                                  Brushes.Goldenrod
                                            };

    static string[] BrushName = new string[] {    "OliveDrab",
                                                  "ForestGreen",
                                                  "DarkCyan",
                                                  "LightSlateGray",
                                                  "RoyalBlue",
                                                  "SlateBlue",
                                                  "DarkViolet",
                                                  "MediumVioletRed",
                                                  "IndianRed",
                                                  "Firebrick",
                                                  "Chocolate",
                                                  "Peru",
                                                  "Goldenrod"
                                             };

    private static Color BackColor = Color.White;
    private static Pen BorderColor = Pens.DarkGray;
    private static int Width = 52;
    private static int Height = 21;

    private Random _random;
    private string _code;
    private int _brushNameIndex;


    override protected void OnInit(EventArgs e)
    {
        //
        // CODEGEN: This call is required by the ASP.NET Web Form Designer.
        //
        //InitializeComponent();
        //base.OnInit(e);
    }

    /**/
    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
        //this.Load += new System.EventHandler(this.Page_Load);
    }



    /// <summary>
    /// 
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    public void Page_Load(object sender, System.EventArgs e)
    {
        if (!IsPostBack)
        {
            //
            // TODO : initialize
            //
            this._random = new Random();
            this._code = GetRandomCode();

            //
            // TODO : use Session["code"] save the VerifyCode
            //
            Session["code"] = this._code;

            //
            // TODO : output Image
            //
            this.SetPageNoCache();
            this.OnPaint();
        }
    }




    /**/
    /// <summary>
    /// 设置页面不被缓存
    /// </summary>
    private void SetPageNoCache()
    {
        Response.Buffer = true;
        Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);
        Response.Expires = 0;
        Response.CacheControl = "no-cache";
        Response.AppendHeader("Pragma", "No-Cache");
    }

    /**/
    /// <summary>
    /// 取得一个 4 位的随机码
    /// </summary>
    /// <returns></returns>
    private string GetRandomCode()
    {
        return Guid.NewGuid().ToString().Substring(0, 4);
    }

    /**/
    /// <summary>
    /// 随机取一个字体
    /// </summary>
    /// <returns></returns>
    private Font GetFont()
    {
        int fontIndex = _random.Next(0, FontItems.Length);
        FontStyle fontStyle = GetFontStyle(_random.Next(0, 2));
        return new Font(FontItems[fontIndex], 12, fontStyle);
    }

    /**/
    /// <summary>
    /// 取一个字体的样式
    /// </summary>
    /// <param name="index"></param>
    /// <returns></returns>
    private FontStyle GetFontStyle(int index)
    {
        switch (index)
        {
            case 0:
                return FontStyle.Bold;
            case 1:
                return FontStyle.Italic;
            default:
                return FontStyle.Regular;
        }
    }

    /**/
    /// <summary>
    /// 随机取一个笔刷
    /// </summary>
    /// <returns></returns>
    private Brush GetBrush()
    {
        int brushIndex = _random.Next(0, BrushItems.Length);
        _brushNameIndex = brushIndex;
        return BrushItems[brushIndex];
    }



    /**/
    /// <summary>
    /// 绘画事件
    /// </summary>
    private void OnPaint()
    {
        Bitmap objBitmap = null;
        Graphics g = null;

        try
        {
            objBitmap = new Bitmap(Width, Height);
            g = Graphics.FromImage(objBitmap);

            Paint_Background(g);
            Paint_Text(g);
            Paint_TextStain(objBitmap);
            Paint_Border(g);

            objBitmap.Save(Response.OutputStream, ImageFormat.Gif);
            Response.ContentType = "image/gif";
        }
        catch { }
        finally
        {
            if (null != objBitmap)
                objBitmap.Dispose();
            if (null != g)
                g.Dispose();
        }
    }

    /**/
    /// <summary>
    /// 绘画背景颜色
    /// </summary>
    /// <param name="g"></param>
    private void Paint_Background(Graphics g)
    {
        g.Clear(BackColor);
    }

    /**/
    /// <summary>
    /// 绘画边框
    /// </summary>
    /// <param name="g"></param>
    private void Paint_Border(Graphics g)
    {
        g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);
    }

    /**/
    /// <summary>
    /// 绘画文字
    /// </summary>
    /// <param name="g"></param>
    private void Paint_Text(Graphics g)
    {
        g.DrawString(_code, GetFont(), GetBrush(), 3, 1);
    }

    /**/
    /// <summary>
    /// 绘画文字噪音点
    /// </summary>
    /// <param name="g"></param>
    private void Paint_TextStain(Bitmap b)
    {
        for (int n = 0; n < 30; n++)
        {
            int x = _random.Next(Width);
            int y = _random.Next(Height);
            b.SetPixel(x, y, Color.FromName(BrushName[_brushNameIndex]));
        }

    }
}
